1. Field of the Invention
Method for producing glass laminates having soundproofing properties by adhesively bonding glass sheets to at least one thin layer which has a low plasticiser content and is based on polyvinyl acetal, and to at least one further layer formed from plasticiser-containing polyvinyl acetal.
2. Background Art
The present invention relates to a method for producing laminated glass sheets by combining layers having different plasticiser content based on polyvinyl acetals having different affinity to plasticisers with subsequent migration of the plasticiser between the layers.
To produce laminated glass sheets having soundproofing or penetration-proof properties, film laminates comprising a plurality of layers based on plasticiser-containing polyvinyl acetals are known. The layers in these film laminates, depending on the field of application, have different mechanical properties. In general, a film laminate for producing soundproofing glazings thus has a middle layer that is soft compared to the outer layers. Penetration-proof film laminates may have a reversed structure.
The production of film laminates by combining PVB sub-films is known from WO 03/097347 A1, EP 0566890 B1 and EP 0508864 B1. Here, sub-films formed from identical PVB polymers containing different plasticisers are combined (WO 03/097347 A1, EP 0508864 B1) or PVB polymers having a high residual acetate content are used (EP 0566890 B1).
In these publications, the combination of a plurality of layers based on plasticiser-containing polyvinyl acetals is proposed for the production of film laminates. Since polyvinyl acetal with a high plasticiser content is very sticky and is soft (that is to say mechanically unstable), combining layers formed from this material is a difficult process. In industrial practice, the production of soundproofing film by means of co-extrusion has therefore prevailed. Here, the sticky layer with high plasticiser content, low glass transition temperature, high ductility and a mechanical damping maximum in the region of room temperature is surrounded by two layers of less sticky PVB film, such that the handling of such a tri-layer film when winding and unwinding, when placing onto glass, etc., is largely determined by the properties of the two external layers of PVB film of normal softness. By contrast, the handling of a thin PVB layer with a high plasticiser content and a glass transition temperature below 10° C. would be impossible from practical viewpoints due to its strong stickiness and excessively low tensile strength.
Co-extruded soundproofing films can be well handled and laminated between glass sheets. A significant disadvantage becomes apparent with these multi-layer products due to their highly restricted ability to be recycled. The unequal distribution of plasticiser between the film layers in contact with one another, necessary to maintain two different glass transition temperatures, requires a difference in polarity of the polyvinyl acetals used in the respective layers, said difference in polarity being set generally by different residual acetate content and/or degree of acetalisation of the polyvinyl acetal. The difference in polarity however means that the polyvinyl acetals can no longer be mixed without phase separation, which, in the case of re-extrusion, leads to milky clouding of the film thus produced.
A further disadvantage lies in the particularly high costs of the mentioned multi-layer films, obtained by co-extrusion, when these are to have further functions, which are likewise introduced into the product by special method variants. In particular, the combination with an ink ribbon additionally extruded in, or the combination with a wedge-like course of the thickness profile of the film web, or both leads to considerably increased production costs, which are passed on in the market.
The problem addressed by the present invention was therefore to provide a method, by means of which glass laminates having good acoustic properties can be obtained, without having to revert to a co-extruded multi-layer film or to a soft damping layer, which is difficult to process. A further problem was to provide cost-effective alternatives for producing glass laminates having combined properties (colour tint, with wedge-shaped thickness profile for head-up, acoustics), with which it is currently necessary to revert to costly special PVB films.